Near field communication (NFC) devices that are configured according to ISO 18092, ISO 14443 and ETSI allow bidirectional communication between two devices based on RF technology. These devices can feature different operating modes including: tag emulation, NFC peer to peer and reader/writer mode. Proximity coupling devices (PCD) include a circuit that emits an electromagnetic field that powers a proximity integrated circuit card (PICC) (e.g., a tag or transmitter) by inductive/magnetic coupling.
The antenna of a PCD consists of an inductor Lr that emits the magnetic field that is used both to power the (passive) PICC, and to carry the data during transmission via mutual inductance M. To make the PCD transmitter energy efficient, the antenna inductor can be combined with a capacitive network Cr, such that the antenna is part of a resonator. For efficient power transfer from the PCD to the (often battery-less) PICC, as well as for energy efficiency of the PCD itself, the PCD's antenna resonator can be tuned to the carrier frequency used in transmission. A resistor Rr can provide dampening in order to increase the transmit bandwidth. The voltage across this resistor can also be used to detect the signal emitted by the PICC (typically using load modulation).
Applications based on inductively-coupled radio frequency identification technologies have evolved from simple presence detection to more advanced applications such as electronic passports and ticketing, contactless smartcards and NFC communication in mobile phones. This evolution comes with a demand for increased data rates, which led to recent proposals to amend the ISO/IEC 14443 (proximity coupling) standard to support data rates of several Mbit/s. Combining the increased data rates with an energy efficient antenna structure is a challenging task.